1. Field of Invention
The present invention concerns an improved process to reduce the number of defects in a Group III nitride (e.g. GaN) with a corresponding improvement in the electrical, optical and mechanical properties of the formed nitride. Specifically, reduction is achieved when the thin layer is first formed at low pressure, then subjected to further formation using a higher pressure (with alternating use of low pressure and high pressure as needed).
2. Background Art and Related Art Disclosures
Prior art in the metalorganic chemical vapor deposition (MOCVD) growth of III-V nitride thin films typically use a single low temperature buffer layer for nucleating the film growth. The reactor pressure is typically atmospheric pressure or low pressure (100 torr or less).
For general information, see for example:
S. Nakamura et al., Applied Physical Letters, vol. 64 (#13), p. 1687-1682 (28 Mar. 1994) discloses the use of conventional MOCVD to produce candela-class high brightness InGaN/AlGaN double-heterostructure blue-light-emitting disorders. PA1 H. Amano, et al., in Japanese Journal of Applied Physics, vol. 29 (#2), pp. L205-L206 (February 1990) disclose the preparation of GaN film grown on sapphire by conventional metal organic vapor phase epitaxy (MOVPE). The layer has room temperature stimulated emission near UV. This indicates the GaN film is promising as a UV laser diode. PA1 D. Hess et al. in U.S. Pat. No. 4,863,755, describe the general and accepted chemical vapor deposition apparatus, configuration, and technique to produce thin films. PA1 (a) combining under metalorganic chemical vapor deposition (MOCVD) conditions at least one Group III metalorganic compound with ammonia, hydrazine, nitrogen-hydrogen, alkylamine or combinations thereof in a III/V molar ratio of between about 1/10000, and 2/1 (metalorganic/ammonia, hydrazine, nitrogen-hydrogen, alkylamine, or combinations thereof) at a low pressure of about 100 torr or less, to produce a first Group III nitride layer for between about 5 and 60 min; PA1 (b) combining under metalorganic chemical vapor deposition conditions at least one Group III metalorganic compound with ammonia, hydrazine, nitrogen-hydrogen, alkylamine or combinations thereof in a ratio of between about 1/10000 and 2/1 (metalorganic/ammonia, hydrazine, nitrogen-hydrogen, alkylamine or combinations thereof) at a high pressure of about 700 to 10,000 torr for PA1 (c) repeating steps (a) and (b) to produce a Group III metal nitride, having a reduced defect density of less than half of the defects obtained compared to a Group III metal nitride is produced wherein high and low pressure cycling is not used.
Properties of Group III Nitrides, by James H., Edgar, ed., INSPEC, the Institution of Electrical Engineers, London, United Kingdom, 1994, describe many aspects of nitride structure, including defects. Chemical vapor deposition (CVD) and metalorganic chemical vapor deposition (MOCVD) are known in the art. Additional references of interest as background to assist one of skill in this art include U.S. Pat. Nos.: 5,402,748; 5,379,720; 5,343,055; 5,305,341; 5,296,088; 5,268,039; 5,196,372; 5,179,042; 5,154,949; 5,141,893; 5,141,569; 5,106,453; and 5,082,798.
All references, articles, papers, patents, standards, etc. cited in this application are incorporated herein by reference.
No reports on varying the pressure of the process during the growth with the intent of reducing the defect density have been reported.
It is therefore apparent that a need exists for an improved process to reduce the defects in Group III nitrides and to improve desirable properties. The present invention accomplishes these objectives.